It is often desirable to monitor a mobile subject so that the mobile subject may be contained within a selected boundary, and to identify when the mobile subject has left such a boundary. A conventional method of monitoring the movement of a mobile subject and detecting whether the mobile subject has left a selected boundary, or containment area, is the employment of a GNSS fencing system.
Various conventional GNSS fencing systems, which employ GNSS systems such as the Global Positioning System (GPS) of the United States, the Russian GLONASS, etc., have been typically used to define the boundaries of a selected containment area and monitor the movement of a mobile subject relative to the selected containment area. In such systems, the position and speed of the mobile subject to be confined are monitored through the use of the GNSS satellites to determine if and when the mobile subject crosses a boundary. Typically, a mobile device to be provided to the mobile subject is used to program the boundary of the selected confinement area as the device is moved along such boundary. Alternatively, the coordinates of the boundary vertices may be programmed directly into the mobile device. If the mobile subject provided with the mobile device crosses the boundary, a corrective stimulus can be provided to the mobile subject.
These conventional GNSS fencing systems typically employ differential GNSS to improve the perceived position and speed of a mobile subject. Such a practice improves the accuracy of determining the mobile subject's position when compared to a non-differential system by incorporating pseudo-range (or distance) corrections for each satellite observable in the mobile subject's position solution. These pseudo-range errors arise due to variations in the atmosphere or signal path for each satellite signal as the signal travels to a receiver provided to the mobile subject. The pseudo-range corrections are computed by a fixed GNSS receiver at a known location, and communicated to the mobile subject receiver over a suitable communication link.
Conventional GNSS position and speed determining systems perform best in fencing or boundary detection applications when favorable signal conditions exist. However, anomalies in GNSS tracking occur even under optimal conditions. Unfavorable signal conditions may exist at the location of the mobile subject that do not exist at the fixed GNSS receiver, and therefore are not recognized as such by the fixed GNSS receiver. In situations in which unfavorable signal conditions exist, errors produced while determining position and speed frequently result in a false boundary violation. Such false boundary violations may erode consumer confidence, and/or may have a negative psychological effect on mobile subjects which are provided with the mobile device to restrict the mobile subject's movement to within the containment area. For instance, if the mobile subject is a pet, such as a dog, which may receive a corrective stimulus as a result of determining that a boundary has been violated, receiving the corrective stimulus while not actually violating the containment boundary may disrupt the training process.
As such, there exists a desire for a mobile position determining apparatus that can recognize, quantify, and mitigate position and speed errors, especially under unfavorable GNSS signal conditions, for the purpose of reducing the probability of false violation determinations.